The ‘Nebular Hypothesis’ is one of the earlier concepts, Trying to understand the Origin of Earth and the Universe, Propounded by the French mathematician Pierre-Simon Laplace in his book Entitled ‘Expositions of the World System‘ in the Year 1796.
According to ‘Nebular Hypothesis’, The Sun and the Planets are Formed By the Hot rotating cloud of gas and Dust which he called as Nebula.
Laplace Nebular Hypothesis is similar to the Kant’s Gaseous Hypothesis but Laplace Fixed the Defects in Gaseous Hypothesis and Presented its Modified Version.
What are the Defects in the Kant's Hypothesis?
There were 3 Basic Defects in the Kant’s Gaseous Hypothesis
1. Large amount of Heat cannot be Generated by the Collision of Cold Particle of Primordial matter.
According to Kant, when two cold Particles in the space collided with each other in space, with their collision they got extremely hot which is not acceptable.
2. Mutual Collision of particles cannot generate motion in the matter and their random motion cannot became a circular motion.
we can assume that due to collision random motions can be generated but how they all got into a circular motions. Kant was not able to explain that.
3. The speed of Nebula was increasing with increase in its size
According to Physics law of angular momentum if nebula is getting bigger then its speed should be decreasing but according to Kant, it was Increasing.
To Remove these Defects Laplace took 3 assumptions to Postulate his Hypothesis
1. He assumed that there was a hot and huge gaseous nebula in the space.
2.The hot and huge gaseous nebula was rotating (spinning) on its axis.
3.Due to the process of radiation, the nebula was getting hot in center and colling down on its border, and due to cooling it was breaking and nebula size was decreasing and if the size is decreased then it will rotate (spin ) faster and all this process also become fast. All it means that nebula was contracting.
When the Hot Gaseous nebula was rotating on its axis, there was some process going on
1.Particles of premordial matter was attracting each other(Due to Gravity) and getting fused(joining) with each other.
2. Due to the Centripetal Force lighter elements like Hydrogen and Helium getting pushed inside. our sun is made up of hydrogen and helium.
3.The centrifugal force pushed the heavier elements to the border or at outside.
These process made The nebula a disk shaped and the lighter elements collected in the center became the (Proto-Sun). As nebula get so contracted and fast that the center part( proto-sun ) broke from the outer surface The Remaining outer part or the ring later took the shape of 9 Planets.
Criticisms of the Nebular Hypothesis-
Laplace Hypothesis commanded Great respect for more then 150 years. But as the time passed and knowledge of science and tech increased.His Hypothesis Started to Get Criticized and Get Rejected .
Lets have a look at Points For which he is criticized
1. Laplace assumed that initially there was a hot and huge rotating nebula, but he was not able to explain the source of origin of that nebula.
2. Why 9 planets came out of the ring or the outer part? Why not a one big planet or more then 9? He was not able to explain this.
3. Why the process of cohesion stopped? why aren’t new planets are forming? why the process stopped? No explanation.
4. If sun was formed during this process it should also have a bulge in its center like other planets. He was also not able to explain this.
5. If planets were initially in the gas or liquid state, it is not possible that they can mention their current shape and orbit. only a solid mass can maintain an orbit and shape.
6. According to Hypothesis all planets and satellite should rotate in one direction buy why some planets and satellite are rotating opposite?
This Answer is Divided into 4 parts Kant’s Defects, Laplace Assumptions, Explanation and Criticism. Don’t Forget to Divide your answer in different parts for better explanation and understanding. Best of Luck.!! Find more at Physical Geography